Rev Limiter Question

[DickR]

That is called a soft cut or throttle cut.
A hard cut is when the rpm bounce back and forth because ignition cut.

We old timers from the points ignitions and carburetor days had to rely on various ignition cut rev limiters. The most basic types use centrifugal force to short the current to the distributor rotor tip. Google Lucas and Bosch rev limiter rotors if you care. These are NOT "soft" and may contribute to engine wear. I used this type on my Lotus Europa. I could raise the rev limit by drilling holes in the movable shorting bar.

There are also more sophisticated ignition cut rev limiters that control which cylinder gets cut such that the effect is actually pretty smooth. I used a couple of different versions of these on my Formula Ford which had a carb and points.

https://www.pegasusautoracing.com/group.asp?GroupID=IGNREVLIMIT

https://www.google.com/url?sa=i&rct...UUn0nELNOyZs5urnxttJz4TQ&ust=1505873106002007

Note that the commentary with the Lucas pictures gives rpm limits. Those are 1/2 the engine rpm.

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[Blacktop]

It doesn't bounce....the engine just falls flat on it's face once the fuel is cut. There is no holding, it feels like the engine shuts off.

I agree. I have taken my car to redline several times. The dash turns red then a little higher rpm the car just noses over with less power. Its very soft on the engine. There are no harmonics.
From what I understand the TB closes regarless if you are pressing the pedal and the fuel is cut.?
If thats the way it works Thats cool. I think I read above about bouncing off the revlimiter being childish in a way.
I feel if bouncing off the rev limiter makes you happy put that pedal down. Nothing like hearing an engine being used at its max. I have watched many many videos of the coyote motors bouncing everyday and not skipping a beat. There are many failsafes built into the computer strategies. Use it until it breaks.

 

[jasonstang]

Were arguing semantics here, but soft cut limiters are typically refereed to as soft not because they are easy on the engine, but because they allow you to maintain or slow the engines RPM. A hard cut limiter is just that, a limiter that kills the engine temporarily.

Well bouncing action of rpm loan and unload the engine can cause all kinds of issues such as timing chain gears and crank flexing.
The soft cut is a better rev limiter.

 

[millhouse]

Well bouncing action of rpm loan and unload the engine can cause all kinds of issues such as timing chain gears and crank flexing.
The soft cut is a better rev limiter.

If by soft cut you mean fuel cut (a hard cut limiter) then I agree. You just need to update your terminology to match the rest of the auto world.

 

[jasonstang]

If by soft cut you mean fuel cut (a hard cut limiter) then I agree. You just need to update your terminology to match the rest of the auto world.

I am not getting what you are trying to say.
A soft cut is where the rpm just sits there where a hard cut is when the fuel or spark is cut then resumed when the rpm drops below the limiter and then goes back up again and then repeat the process.
S550 has a soft cut to help reducing the stress that hard cut can cause.
If that is not a soft cut what is a soft cut to you?

 

[millhouse]

I am not getting what you are trying to say.
A soft cut is where the rpm just sits there where a hard cut is when the fuel or spark is cut then resumed when the rpm drops below the limiter and then goes back up again and then repeat the process.
S550 has a soft cut to help reducing the stress that hard cut can cause.
If that is not a soft cut what is a soft cut to you?

Soft cut = any rev limiter that keeps the RPM at the limit.

Hard cut = any rev limiter that kills the engine at the limit.

The S550 has a hard cut limiter at 7000rpm. Hit that and the engine dies until RPMs fall.

Hard cut limiters (fuel cut) are gentler on engines...which is why virtually all OEMs use them.

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